It is known to process waste by pyrolysis and gasification in modular waste processing apparatus including separate pyrolysis and gasification units. Pyrolysis is the thermal decomposition of material under the action of heat alone (i.e. in the absence of oxygen), and is an endothermic process. During pyrolysis, a pyrolysis feedstock (such as human or consumer waste) is decomposed to form pyrolysis char and combustible pyrolysis gas.
Gasification is the exothermic reaction of carbonaceous material, such as pyrolysis char, with oxygen and/or steam to produce combustible syngas. Syngas may include hydrogen, carbon monoxide and carbon dioxide.
The resulting pyrolysis gas and syngas can be combusted to provide thermal energy to sustain the pyrolysis process, and any remaining thermal energy can be converted (e.g. to electricity using a generator) or used onsite.
However, known waste processing apparatus for separately conducting pyrolysis, gasification and combustion suffer from a number of problems.
In particular, particulate material such as ash is known to cause problems in previously considered waste processing apparatus. The deposition and build-up of particulates in an oxidiser and downstream of the oxidiser in a heating chamber for the pyrolyser can reduce the performance of the waste processing apparatus and can result in frequent maintenance and down-time of the apparatus to remove the particulate material. For example, deposition of particulate material on a pyrolysis tube within the heating chamber can result in inefficient heat transfer between the hot gas in the heating chamber and feedstock material received in the pyrolysis chamber. Further, particulate material is known to build-up to form a bed of settled particulate material on the floor of the oxidiser and the floor of the heating chamber for the pyrolyser, which is typically removed by opening up the oxidiser and heating chamber respectively.
In addition, in previously considered gasifiers a bed of feedstock material such as pyrolysis feedstock in the gasifier may become agglomerated or caked, which may result in an inefficient gasification process and/or a blockage in the bed.